This invention pertains to the preparation of high molecular weight, thermally stable polyarylates.
Polyarylates, i.e., polymers consisting essentially of aromatic ester units, have previously been prepared from dihydric phenols, such as, Bisphenol-A, i.e. 2,2-bis(4-hydroxyphenyl) propane and terephthalic acid or a mixture of isophthalic and terephthalic acids by first converting the aromatic acids to their acyl chlorides, isolating and purifying them, and then subjecting them to a solution condensation polymerization or an interfacial condensation polymerization with the dihydric phenol. While polyarylates of satisfactory quality are obtained this way, the purification and isolation steps add to the cost of the final product thus limiting their commercial exploitation as extruded and shaped articles, textile fibers, films and the like.
U.S. Pat. No. 4,129,594, issued Dec. 12, 1978, describes the preparation of aromatic dicarboxylic acid chlorides which are used for the direct acylation of bisphenols to produce aromatic polyesters. This patent describes the preparation of terephthaloyl chloride by adding terephthalic acid to a dichloromethane medium containing phosgene and pyridine wherein the pyridine is present in an amount of about 1.1 equivalents per equivalent of carboxylic acid group in the total terephthalic acid employed. The dichloromethane is employed in an amount of from about 10 to 20 parts by weight per part of total terephthalic acid employed. The reaction is carried out at a temperature of about 15.degree. to 30.degree. C. to yield terephthaloyl chloride of at least 97 percent of theory. The terephthaloyl chloride is then reacted with Bisphenol-A to form oligomer products.
However, the preparation of terephthaloyl chloride as described in the aforementioned patent results in purification problems due to the required use of a base in excess of stoichiometry. Furthermore, the polyesters prepared in accordance with the procedures of U.S. Pat. No. 4,129,594, are low molecular weight polyesters.
It is therefore an object of this invention to provide a simple, economic process for the preparation of polyarylates without compromising molecular weight and/or mechanical/physical properties. In this process, the intermediate acid chloride is prepared with a catalytic amount of base.
Another object of this invention is to provide a process for the preparation of polyarylates using inexpensive reactants.
Still another object is to provide polyarylates having a minimum of color therein. Other objects will become apparent to those skilled in the art upon further reading of the specification.